1. Field of the Invention
The present invention relates to an optical module and an optical receiver using the optical module.
2. Related Prior Art
Japanese patent application published as S63-105541 has disclosed one type of an optical receiver, which has an avalanche photodiode (hereinafter denoted as APD), and a PIN photodiode (hereinafter denoted as PIN-PD) that receives light reflected by the APD. This optical receiver controls the bias voltage responding to the output from the PIN-PD.
Another Japanese patent application published as S63-077171 has disclosed another type of the optical receiver. This optical receiver provides a photodiode that includes a first region for receiving signal light and a second region for monitoring primarily the incident power of the signal light. Two photodiodes are formed on the single substrate. The APD is formed in the first region while the PIN-PD is formed in the second region. In this optical receiver, the bias voltage applied to the APD is controlled based on the output provided from the PIN-PD.
In the former optical receiver, the bias voltage applied to the APD is controlled based on the output from the PIN-PD that receives light reflected by the APD. Since the magnitude of the light reflected by the APD depends on the polarization of the light, the output current provided from the PIN-PD also depends on the polarization, whereby the bias voltage applied to the APD varies depending thereon.
In the latter optical receiver, the bias voltage applied to the APD is controlled by the output from the PIN-PD formed in the first region. However, the PIN-PD and the APD are integrally formed in the same substrate, so the output current from the PIN-PD is affected by the APD through the crosstalk.